These critical biochemical and biophysical studies of nucleic acids and polypeptides from RNA tumor viruses will be continued in order of their complexity. 1. Characterize the nucleic acids and the structural polypeptides of purified virions released from cells which have been transformed by sarcoma viruses, 2. determine which of the viral specific polypeptides is the reverse transcriptase of the virions, 3. isolate and characterize the viral specific nucleic acid and polypeptides of cells infected with leukemia and sarcoma viruses, 4. determine what makes a sarcoma virus either competent or defective.